Apodization profiles of fiber Bragg grating spectra in temperature sensor applications

Abstract

The presence of side lobes in the FBG reflection spectrum is a critical challenge that can reduce measurement accuracy in optical sensor applications, necessitating a systematic evaluation of apodization techniques as a mitigation strategy. This study investigated the comparative effects of three apodization profiles, namely uniform, Gaussian, and tanh hyperbolic, on the spectral characteristics and performance of an sensors-based temperature sensor with a grating length of 10 mm, grating period of 0.535 µm, modulation index of 0.0001, and operating wavelength of 1550 nm, over a temperature range of 20°C to 100°C. The results showed that all three profiles produced an identical thermal sensitivity of 13.725 pm/°C with a deviation of 3.23% from the theoretical value of 14.183 pm/°C. The Gaussian profile demonstrated the most superior side lobe suppression with an average side lobe level (SLL) of -45.51 dB, exceeding the minimum standard of -20 dB by more than 25 dB, far surpassing the uniform (-16.90 dB) and tanh (-18.17 dB) profiles. These findings establish the Gaussian apodization profile as the most optimal configuration, delivering the highest spectral quality without compromising thermal sensitivity.